App Extension - How to set the favicon, and API to update the setting schema.

[yinghechen]

Hi Shopify Dev community,

I am developing an app extension, I have trouble finding :

1. How to update/set the app extension favicon, and my app extension shows blank favicon/image in theme editor during the install.

2. How to mutate/update the app extension block setting schema value through the API ? Should I use asset API, and get approval for exemption ? 

(I need this API because users are much easy/instructed to input this value on my app, instead of inputing this value in the theme editor.)

Thank you so much.